The bell shaped plates of rotary sprayers are known and conventionally used for the automatic series production coating of work pieces i.e. (DE 43 06 799). Bell shaped plates can serve as spraying bodies, and can have an externally threaded cylindrical hub section that is manually screwed into the open front end of the hollow shaft of the drive motor. The drive motor can consist of an air turbine, and can be unscrewed, for example, for maintenance purposes or for installing a new bell shaped plate, while the hollow shaft can be appropriately locked i.e. (EP 1 245 290). Since, due to the high speeds of the air turbine, e.g., in the range of more than 50,000 rpm, this detachable mounting device requires that the bell shaped plate be accurately centered and balanced relative to the axis of the hollow shaft, the hub section of the bell shaped plate can include a conical part which lies against a matching conical area of the inside wall of the hollow shaft to form a centering cone. In contrast, the hub section of the bell shaped plate of other known rotary sprayers i.e. (EP 1 266 695) has an internal thread instead, by means of which internal thread the hub section is screwed onto an external thread at the end of the hollow shaft.
In addition to the centering and balancing requirement, the devices for mounting a bell shaped plate on its drive shaft must meet certain other requirements as well, such as tight fit for the reliable transmission of torques in both directions of rotation during acceleration and brake application, small space requirement, low risk of soiling, e.g., due to spray paint mist, easy cleaning, and last but not least, the possibility of rapid and easy mounting and dismounting.
The problem of the prior art rotary sprayers is that during malfunctions, the detachable mounting device can accidentally detach itself. Such accidents can have different causes, e.g., wear of the turbine, damage due to collision of the bell shaped plate with the work piece to be coated or due to inappropriate handling, imbalance of the bell shaped plate due to damage, faulty threading or soiling, etc., and can lead to a sudden abrupt brake application or seizing of the shaft. In the case of a screwed in or screwed on bell shaped plate, depending on the threading direction (right or left), the risk of an accidental detachment of the bell shaped plate may also arise during rapid acceleration of the bell shaped plate. In each case, it is possible for the bell shaped plate, which rotates at a high speed and which, because of its kinetic energy, can unscrew itself, to be flung from the sprayer, which can entail a considerable risk of damage and personal injuries.
To prevent the risk of the bell shaped plate being flung off, the European Patent EP 1 266 695 proposes after the threaded connection has been accidentally loosened, the bell shaped plate be caught by radial projections on the housing, against which the detached bell shaped plate abuts with radial projections of its hub section. The projections of the housing and the bell shaped plate can be twisted with respect to each other in a bayonet type fashion so that the bell shaped plate can be manually removed from and inserted into the sprayer. Since this design does not prevent the self acting complete unscrewing of the threaded connection, the detached bell shaped plate, which as a rule still has considerable kinetic energy and is moved by considerable out-of-balance forces, is able to damage not only the threaded connections but also any other parts of the bell shaped plate itself and of the sprayer.